There is a requirement in the telecommunications industry for optical components which function as switches or attenuators for optical networks. Recently, there has been a great deal of interest in optical switches and attenuators based on MicroElectroMechanical Systems (MEMS). WO 98/12589 describes one such switch which is fabricated from a single substrate. Deep Reactive Ion etching (DRIE) is used to form an actuator and a vertical shutter which can be moved by the actuator into or out of a switching region between the ends of one or more optical fibres held in trenches etched in the substrate, so as to switch an optical signal from one optical fibre to the other by reflection off the shutter. The switching region is filled with index-matching fluid to avoid undesirably high losses due to mismatch of refractive indexes in the switching region. The whole switch therefore needs to be sealed from the environment, in order to contain the index-matching fluid within the switch. A disadvantage of this type of device is that there is the possibility of leakage from the package. Moreover, the packaging of such a fluid-filled package is a very complex operation. Also, the long term stability and thus performance of such index-matching fluids is not fully known.
In order to allow greater potential for integration of active and passive optical components, there is however a desire to move away from fibre-based components, to components made using planar waveguide technology. U.S. Pat. No. 6,195,478B describes an optical switch based on planar waveguide technology. In this switch a shutter formed using MEMS technology can be displaced (by a MEMS actuator) along a trench formed between at least two waveguide ends, to effect switching of an optical signal from one waveguide to another by reflection off the shutter. In one embodiment the trench is filled with index-matching fluid, and so again the whole switch needs to be enclosed in an outer package to contain this fluid therein. In other embodiments, the trenches are filled only with air, but even in these latter embodiments it is necessary to seal the whole switching component hermetically from the surrounding environment, in order to protect the delicate structure of the MEMS components from damage from moisture, small particles or other environmental contaminants. This present significant problems, for example this requires the outer package for the device to be made from specific materials known to provide hermetic sealing, and for complex package sealing operations to be performed by skilled operators in order to meet industry hermetic package requirements. Additionally there is the problem that such a hermetic package restricts the type of materials which can be used inside the package: because nothing can pass into the package or out of the package, therefore nothing can be contained inside the package that would cause harm.
Moreover, in order to seal the contents of the package from the external environment this requires all signal entrance and exit ports (normally in the form of input and output fibres passing through walls of the package) of the packaged end component to be sealed as well and this can be technically challenging, particularly (but not exclusively) where hermetic sealing is required, and hence costly and time-consuming for components having a high port count. Also, this requirement tends to increase the risk of component failure (if any of these port seals fail). Moreover, such port sealing can place undesirable stress on the input/output fibres and so some stress release mechanism may have to be built into the package to avoid this problem. These factors all contribute to undesirable expense and complexity in the manufacture of the end product.
It is an aim of the present invention to avoid or minimise one or more of the foregoing disadvantages.